(function() {
	function screenZoom() {
		var deviceWidth = document.documentElement.clientWidth;
		if(deviceWidth > 640) {
			deviceWidth = 640;
		}
		document.documentElement.style.fontSize = deviceWidth / 6.4 + 'px';
	}
	screenZoom();
	window.onresize = function() {
		screenZoom();
	}
})();